Mechanics of Breathing II Flashcards
How is airflow calculated?
Airflow (V) = Δ Pressure (P) / Resistance (R)
More resistance means what to air flow?
it will be lower
how can resistance in airflow be overcome?
increasing pressure difference between two ends
hagen-poiseuille equation
Resistance (R) α 1/radius4
two types of airflow
laminar and turbulent
what is loss of patency?
closing or obstruction
what is the open structure of airways maintained by?
elastic fibres within the wall of the airway and radial traction
why is airway obstruction more noticeable in expiration?
lung tissue and airways are compressed
what happens when intrapleural pressure becomes positive?
collapsing force will be exerted onto airways
how is spirometry calculated?
FEV1/FVC
how is spirometry measured?
patient produces max forced expiration plotted on a graph
what is FEV1
forced expiratory volume in 1 second
what is FVC
forced vital capacity
obstructive airway diseases
asthma and chronic bronchitis
what will change in the ratio for obstructive diseases
FEV1 decreases and so will the ratio
restrictive lung diseases
pulmonary fibrosis, indicated by reduction in FEV1 and FVC so ratio is normal
what does difference between pressure within alveoli and intrapleural space determine?
level of force acting to expand or compress the lungs
what happens to intrapleural pressure in inspiration?
increasingly negative because lung volume increases due to elastic properties
high lung compliance?
less elastic recoil = less force required to inflate = more volume change per pressure change
low lung compliance?
more elastic recoil = more force required to inflate = less volume change per pressure change
how is compliance calculated?
compliance = Δvolume / Δpressure
low compliance
stiff, pulmonary fibrosis. greater pressure change required to produce same change in volume
high compliance
floppy, emphysema. smaller pressure change required to produce same change in volume
effect of fibrosis on compliance?
decreased compliance
lung = stiff
effect of COPD on compliance?
increased compliance
lung = plastic bag
what creates a bubble?
water-air interface between lining fluid and psuedo-spherical alveolar airspace
what creates surface tension in the bubble?
relative strength of hydrogen bonds between water molecules combine to exert overall collapsing force towards centre of bubble
what does collapsing force in water-fluid interface do?
generates pressure
what is law of laplace?
calculates pressure generated within the bubble
law of laplace
P = 2T/r
If T remains constant
P α 1/r
relationship between pressure and bubble radius
inversely proportional
smaller bubble
= greater pressure
what happens to smaller alveoli due to pressure gradients
they collapse into larger ones
how is problem of smaller alveoli collapsing solved?
pulmonary surfactant, phospholipoprotein secreted by type II pneumocytes
structure of surfactant molecules
amphipathic with hydrophilic head and hydrophobic tail regions
what will presence of surfactant do?
disrupt attractive forces between water molecules reducing surface tension and collapsing pressure generated
what does increase in alveolar size do to concentration of surfactant molecules?
decreases at interface
what happens where pulmonary surfactant is present?
surface tension increases with increasing alveolar surface tension so air naturally flows from larger alveoli to smaller ones
what does surface tension do to hydrostatic pressure in alveolar tissue
reduces hydrostatic pressure in alveolar tissue. pulls fluid out of surrounding pulmonary capillaries into alveoli and interstitial tissue
what does reduced surface tension mean?
pulmonary surfactant prevents alveolar oedama due to excessive fluid being pulled from capillaries
NRDS
neonatal respiratory distress syndrome
what is NRDS
condition in premature infants who develop insufficient levels of pulmonary surfactant resulting in resp failure due to alveoli collapsing = increased lung compliance = alveolar oedema = reduced gas exchange
NRDS treatment
supplementation with artificial surfactant or glucocorticoids to mothers at risk
premature birth/material diabetes –> insufficient surfactant production
–> stiff lungs, alveolar collapse –> resp failure –> hypoxia –> pulmonary vasoconstriction
If more resistance is generated in a patient’s airways, what effect will this have on airflow (assuming there is no increase in respiratory effort)?
Airflow will decrease as airway resistance and airflow are inversely proportional, an increase in resistance will cause a decrease in airflow.
If the radius of a patient’s airways increases (e.g. due to smooth muscle relaxation), what effect will this have on airflow?
Airflow will increase as airway resistance and airway radius are inversely proportional (increase in radius = decrease in resistance), and airway resistance and airflow are inversely proportional (decrease in resistance = increase in airflow). Therefore radius and airflow are effectively proportional (increase in radius = increase in airflow).
pathological features/factors that increase airway resistance.
Contraction of airway smooth muscle will constrict the airway, reducing airway lumen radius and increasing resistance
Mucus hypersecretion will obstruct airways, reducing airway lumen radius and increasing resistance
Increased airflow turbulence generates a greater level of airway resistance than laminar flow
Decreased radial tration will reduce the degree to which the airways are ‘pulled’ open by their connections to the surrounding elastic lung tissue, potentially leadin to reductions in airway patency (the degree to which they are ‘open’).
Loss of patency and collapse of the airway’s structural integrity will clearly obstrcut the airway, increasing resistance and limiting airflow.
A 50 year old woman of 162cm height attends a respiratory clinic to have spirometry measurements taken. The following readings are generated:
FEV1 = 2.6L (expected = 2.7L)
FVC = 3.2L (expected = 3.2L)
Calculate the patient’s FEV1/FVC ratio and utilise it, along with the other readings, to answer the following question:
What kind of respiratory disease are these findings indicative of?
The readings are normal
FEV1 = 96% of expected (>80% = healthy)
FVC = 100% of expected (>80% = healthy)
FEV1/FVC ratio = 2.6/3.2 = 81% (>70% = healthy)
- Which of the following bubbles generates more collapsing pressure:
Bubble A: radius = 4
Bubble B: radius = 2
Bubble B
If the two bubbles referred to in the previous question were suddenly connected – what would happen?
The smaller bubble would empty into the larger one
Assuming the molar quantity of surfactant remains constant, what would you expect to happen to the collapsing pressure generated within an alveoli, as the alveoli increases in radius and size during inflation?
Collapsing pressure within the alveoli will increase as the radius increases
What changes would you expect in lung function if there is insufficient production of pulmonary surfactant (such as in neonatal respiratory distress syndrome)?
Decreased Compliance
Decreased Inspiratory Capacity
Increased Respiratory Effort is Required
Increased Surface Tension at the air-liquid interface
Increased Pulmonary Capillary Permeability
do 100 x FEV1/FVC
this is the % of total lung capacity a person can exhale in the first second (if this value is less than 70% then this implies obstructive airway disease like asthma as it increases resistance but if this value is more than 80% then it’s restrictive airway diseases like fibrosis because compliance decreases)
What is transpulmonary pressure?
- The level of force being exerted to expand the lung/change lung volume
- Reflects the difference between Palv and PIP
What is the transpulmonary pressure if Palv = 0 and PIP = -10?
- Transpulmonary pressure (PTP = Palv - PIP)
- PTP = 0 – (-10) = +10
